Why Flax Takes to the Dye Pot So Well

There is something deeply satisfying about the full circle: sowing a patch of flax in spring, pulling it in summer, retting and breaking it, then spinning the fibres into a yarn you eventually plunge into a steaming pot of onion skins. Homegrown flax gives you a yarn with real character — slubs, the occasional thick-and-thin, a crisp handle that softens with every wash. It is not the uniform stuff of commercial cones, and that is precisely the point.

Linen is a cellulose fibre, which means it behaves quite differently from wool in the dye pot. It has no scales to grab hold of colour, so it needs a mordant to act as a bridge between fibre and dye. Alum is the reliable choice, and if you mordant carefully and dye in small batches, handspun flax will hold colour beautifully — often paler than wool at first, but remarkably lightfast once it has had a few weeks to settle.

Scouring and Mordanting Before You Dye

Flax carries a good deal of pectin and natural wax, and handspun yarn may still hold spinning oils, so scouring is not optional. Work on roughly 100g bundles tied loosely in at least four places so the yarn does not tangle.

• Scour: simmer gently for 45 minutes in water with a teaspoon of soda ash and a drop of washing-up liquid per litre. Rinse until the water runs clear.
• Mordant: use alum at around 8% of the dry weight of the fibre, plus 6% cream of tartar. Dissolve fully in hot water, add the wet yarn, and hold at 80°C for an hour.
• Rest: leave the yarn in the cooling mordant bath overnight. This step makes far more difference to the final depth of colour than most people expect.

Always weigh your yarn dry, before scouring, and write that number down. Every recipe from here on is a percentage of that figure.

Onion Skins: The Everyday Gold

Brown onion skins are the most generous dye in the kitchen. Save them in a paper bag through the winter — you want roughly the same weight of skins as of dry yarn for a strong gold, or half that for a soft honey tone. Red onion skins give a disappointing dull olive on linen, so keep them for the compost.

Simmer the skins in plenty of water for 45 minutes, then strain them out. Some dyers leave the skins in the pot, but on linen the bits cling stubbornly and are tedious to pick out later. Add your damp, mordanted yarn to the strained liquor and hold it at 80°C for an hour, stirring gently and often. Turn off the heat and let the yarn cool in the bath overnight. You will pull out warm apricot-golds that vary from skein to skein depending on where they sat in the pot.

Madder Root: Patience for Reds

Madder is the classic red dye of European textiles, and it rewards restraint. Use 50–100% of the dry weight of the fibre, pre-soaked overnight in warm water — this releases the colour more evenly and avoids a gritty bath. Hard water suits madder; if yours is soft, add a teaspoon of calcium carbonate or a pinch of chalk.

The crucial detail is temperature. Keep the bath below 60°C. Above that, the lovely coral and brick reds slide towards dull brown and stay there. Hold the yarn at 55–60°C for 45 minutes, stirring carefully, then let it cool completely in the liquor — often another twelve hours. The colour will deepen as it cools, so do not panic if the first ten minutes look disappointing.

Small Batches, Big Variations

Dyeing in one- or two-skein batches is where the magic lives. No two pots behave identically, and that is a feature rather than a flaw.

• Exhaust baths: the second and third dips from the same onion liquor give successively paler golds — perfect for weaving stripes.
• Overdyeing: a madder bath over an onion-gold skein produces rich terracotta and rust tones that are hard to achieve any other way.
• pH shifts: a splash of vinegar brightens onion gold; a pinch of soda ash pushes madder towards a deeper crimson-purple.

Keep each batch labelled, and keep a skein from every pot. A row of them on a shelf becomes your own reference library.

Rinsing, Softening and Keeping Records

Rinse in water of a similar temperature to the bath, warming it gradually if needed, or the shock can felt the surface of the flax. Rinse until the water is clear, then dry in the shade — strong sun will fade fresh colour. A final soak in lukewarm water with a little olive-oil soap softens handspun linen noticeably before you wind it into balls.

Finally, keep a notebook. Record the date, the weight of fibre, the mordant percentages, the dye quantity, the top temperature, and how long the yarn stayed in the pot. Two years from now, when you are holding a skein of exactly the gold you want, you will be grateful you did.